1. Field of the Invention
This invention relates to a dot printer, and more particularly, to a printer which does not use any type, or require any ink ribbon.
2. Description of the Related Art
An ink ribbon has usually been used in a dot printer to transfer ink onto a recording medium to form letters, etc. thereon. A printer using an ink melted by heat has been of the kind using types, since the ink is required to dry quickly. It has a type stocker not shown, but keeping a stock of types xe2x80x98axe2x80x99 for letters, symbols, etc. to be printed, and a type wheel xe2x80x98bxe2x80x99 on which types for letters, symbols, etc. to be printed can be mounted, so that the types xe2x80x98axe2x80x99 required for printing may be taken out of the type stocker manually, and mounted on the type wheel xe2x80x98bxe2x80x99, as shown in FIG. 2. For printing, the type stocker and the type wheel xe2x80x98bxe2x80x99 are heated by a heater xe2x80x98cxe2x80x99 so that the types xe2x80x98axe2x80x99 may be heated, and an ink roller xe2x80x98dxe2x80x99 holding an ink melted by heat is heated by a heater xe2x80x98exe2x80x99 to have the ink melted. The types xe2x80x98axe2x80x99 are brought into contact with the ink roller xe2x80x98dxe2x80x99 to have their surfaces coated with the ink, and transfer the ink onto a printing medium xe2x80x98gxe2x80x99 conveyed by a printing medium feed roller xe2x80x98fxe2x80x99. The ink transferred onto the printing medium xe2x80x98gxe2x80x99 is allowed to cool and solidify immediately at room temperature to form letters, etc. The types xe2x80x98axe2x80x99 on the type wheel xe2x80x98bxe2x80x99 are changed to those which are taken out of the type stocker manually as required and are mounted on the type wheel xe2x80x98bxe2x80x99 by any change of the matter to be printed.
A printer using an ink ribbon as a source of ink supply is, however, expensive to maintain, since it requires a frequent change of ink ribbons. A type printer has been large and very expensive, since it is required to keep a stock of many types in its type stocker and requires a mechanism for changing types. Moreover, a change of types has required a complicated manual job bringing about an increase of cost.
According to this invention, there is provided a dot printer which comprises an ink holding member, a platen having an outer peripheral surface coated with ink by contacting the ink holding member, and a printing head facing the platen in an appropriately spaced apart relation thereto. The printing head is a dot impact type printing head having a plurality of printing wires caused to project selectively to form letters, and a recording medium is conveyed between the printing head and the platen to have printing made thereon by the printing head. The printing head, which is of the dot impact type, does not require any complicated job for mounting or changing types. The printer can form uniform dots easily and is easy to supply with ink, since the dots are formed by the printing wires projecting and pressing the recording medium against the ink-coated outer peripheral surface of the platen.
A protective film may be situated between the printing head and the recording medium for protecting the recording medium. It protects the recording medium from any damage caused by the printing wires projecting against it.
The ink holding member may hold an ink melted by heat, and the ink holding member and the platen may each be provided with a device for heating the ink to its melting temperature. The ink melted by heat is easy to handle, since it readily solidifies at room temperature after its transfer onto the recording medium.
The ink holding member is preferably an ink roller having a source of heat located inside, and a member surrounding it and impregnated with the ink melted by heat, since it is easy to handle, or change to a new one in the case of ink shortage, etc.
The apparatus of this invention as described is small and inexpensive, as it does not require any large mechanism for changing types, etc. It does not require any complicated job for mounting or changing types, etc., but can easily form uniform dots, and is easy to supply with ink. A protective film can be relied upon for protecting the recording medium from any damage caused by the printing wires projecting against it. An ink melted by heat is easy to handle, as it readily solidifies at room temperature after its transfer to the recording medium. An ink roller is easy to handle, and easy to change to a new one when it has run short of ink. A drastic reduction of printing time can be obtained if there is a frequent change of the matter to be printed.